1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to electrical and/or atomic force microscopy probe systems.
2. Description of the Related Art
Atomic force microscopy (“AFM”) generally involves scanning a stylus or probe across a microscopic topography, such as an integrated circuit structure, and sensing the forces exerted on the stylus. The stylus is provided with a small geometry tip that physically contacts the surface topography. The tip may be made from conducting or semiconducting materials that enable various types of circuits to be electrically as well as topographically probed.
The technique has been widely used in metrology of structures in photoresist, interlevel dielectric layers, sidewall angles, trench depths and surface morphology. The scanning resolution of the probe is dependent on the radius of curvature of the probe tip that contacts a given topographical feature.
In conventional AFM machines, the probe tip is part of or otherwise fastened to a cantilever that is, in turn, coupled to a base. The base is fitted to a piezo actuator that is operable to move the base, and thus the cantilever along three axes of movement. The piezo actuator is coupled to a moveable carriage that is operable to provide large scale movements of the base, on the order of tens of millimeters. These large scale movements are necessary to bring the probe tip into proximity with an area of interest on an integrated circuit. More refined movements to bring the tip into contact with the integrated circuit at a specific location are accomplished with the piezo actuator. Conventional piezo actuators have a range of movement of a little less than 100 microns.
Currently produced integrated circuits often have millions of circuit structures compressed into a very small footprint. Despite this dense packing, it is often desirable to probe several circuit structures at the same time. For example, in order to probe the behavior of a field effect transistor, it is desirable to be able to simultaneously probe contacts leading to the source/drains and gate of the transistor. Depending upon the minimum device geometry of the integrated circuit, the spacing between the contacts may be less than a micron.
Although conventional probe cantilevers are themselves relatively small devices, the conventional hardware to hold and position them is not. A conventional piezo actuator and the carriage that holds it typically dwarf current integrated circuits. Furthermore, relative to the sizes of probed structures on integrated circuits, conventional probe cantilevers may also be characterized as large indeed. As a result, it is difficult to position more than one conventional cantilever/probe tip proximate an integrated circuit. In circumstances where closely spaced structures require probing, such as the source/drains and gate referred to above, it may be very difficult to successfully position multiple conventional probe tips proximate the targeted circuit structures.
Unless the trend toward increasing miniaturization of integrated circuits that has prevailed since the early days of semiconductor fabrication somehow reverses in the future, the problems associated with probing micro circuit structures just noted will become even more challenging.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.